According to the United States Census Bureau, the township has a total area of 21.6 square miles (55.9 km2), all land.

It consists mainly of rolling hills and valleys and is drained by the Schuylkill River mostly via the Perkiomen Creek.

Its villages include Fagleysville, Frederick (also in Upper Frederick Township,) Hoffmansville, Layfield, New Hanover, New Hanover Square, and Sassamansville (also in Douglass Township.)

New Hanover has a hot-summer humid continental climate (Dfa) and is in hardiness zones 6b and 7a.

The average monthly temperatures in Layfield range from 30.6 °F in January to 75.3 °F in July.

12.2% of all households were made up of individuals, and 5.1% had someone living alone who was 65 years of age or older.